Your tour operator will most likely allow you to bring more luggage if you ask for a medical accommodation. You'll have to think about the disposal of the used diaper, though. Depending on the type of safari (lodge vs. tent) this might be a bigger or smaller issue.
Other than that, how about external catheters and bags? Or something like the Afex system? I am not a fan of external catheters or similar, but they seem to work for others.
Washable diapers or pads might be hard to wash and dry overnight while on safari. But then again, if you are visiting a place like Kenya, the altitude might help drying diapers overnight.
You might think about how you will deal with hot and humid conditions. While most safaris are in relatively dry climates, often times at high elevations, the safari packages often times include a stay on the coast, which might be on the Indian Ocean with temperatures exceeding 110 degrees F and with very high humidity.
I wish you a fantastic trip!